In the oil and gas industry, controllers are used to control the rate of flow and volume of fluid through a pipeline. Because controllers are used in oil and gas fields, it is important that the controllers be sufficiently rugged to withstand the rigors of such an environment, be self-contained and designed so as not to present a safety hazard, and be sufficiently easy to use to allow relatively unskilled field personnel to operate them. It is also a great convenience not to have the controllers depend upon commercial power systems as their power source. And, above all, the controller must be accurate. Existing controllers do not exhibit this combination of design features. In particular, they tend to be complicated and difficult to use and consume a large amount of power.
Therefore, a need has arisen for an accurate controller which is suitable for use in such rugged environments as the oil or gas industries, which consumes a small amount of power, and which is simple to operate by untrained personnel, yet fully programmable. A further need has arisen for a controller which can be operated remotely.